The steering angle and steering angle lock in motor vehicles are required for influencing a driving dynamics control system. In addition to the steering angle values, this driving dynamics control system obtains further measurement data, such as wheel rotational speed and the rotation of the motor vehicle about its vertical axis. The driving dynamics control system evaluates the absolute steering angle lock and the steering speed values with the other detected data. The driving dynamics control system uses these values and other data for controlling actuators such as brakes and engine management.
DE 4022837 A1 discloses an optoelectronic steering angle sensor. The steering angle sensor includes a light source and a line sensor arranged in parallel and spaced apart from each other. An encoder disc is disposed between the light source and the line sensor. The encoder disc is non-rotatable connected to the steering spindle. The line sensor is a CCD-sensor line. The code transmitter is formed as a light slit disc and as a code trace in the form of a spiral which increases in size from the inside outwards. The exposure of the image points of the line sensor in a specific steering lock makes it possible to obtain information regarding the actual steering angle lock.
An Archimedean spiral extending over 360.degree. provides the coding for this encoder disc. This steering angle sensor determines absolute steering wheel angle positions only in the range of the coding and thus only in the range of 360.degree.. However, it is possible to rotate steering wheels much more than 360.degree.. On the basis of a straight position of the wheels and thus a zero position of the steering angle sensor it is desirable to detect the absolute steering angle in an angular range of the entire rotational range of the steering wheel.
The steering angle sensor disclosed in DE 4022837 A1 only detects an angle segment in the range of a complete steering wheel lock of 180.degree. to the right and 180.degree. to the left starting from the zero position of the steering angle sensor. However, steering wheels in motor vehicles can make, for example, three complete turns to the right and to the left starting from the zero position. Thus, a steering angle sensor which measures in the absolute steering angle position would have to be able to cover 2160.degree., i.e., six revolutions.
Steering angle sensor systems are disposed in the region of the steering spindle of the motor vehicle. The installation space available in this region for installing the steering angle sensor is limited both in the axial direction and, in particular, in the radial direction with respect to the steering spindle. For this reason, an attempt is made to connect steering angle sensor systems to existing modules such as the flat spiral spring cartridge or to integrate them therein. In many cases, this is only possible if the steering angle sensor requires the smallest possible allowable installation space.